Method for integrating a co2 capture unit with the precooling section of a natural gas liquefaction plant

ABSTRACT

A method of simultaneously liquefying CO2 and cooling natural gas, including providing a compressed CO2 loop, comprising a pressurized cooling stream, wherein a first compressed cooling stream and a second compressed cooling stream are produced by a CO2 compressor. Providing at least a portion of the first compressed cooling stream to a CO2 liquefaction system, wherein the first compressed cooling stream provides at least a portion of the refrigeration required by the CO2 liquefaction system. Providing at least a portion of the second compressed cooling stream to the pre-cooling system of a natural gas liquefaction system, wherein the second compressed cooling stream provides at least a portion of the refrigeration required by the natural gas pre-cooling.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority under 35 U.S.C. § 119 (a) and (b) to U.S. Patent Application No. 63/111,297, filed Nov. 9, 2020, the entire contents of which are incorporated herein by reference.

BACKGROUND

Following the pretreatment step that is designed to purify the natural gas feed stream of any impurities that could result in freezing issues at the very cold temperatures downstream, such as water, heavy hydrocarbons, etc., most natural gas liquefaction plants all share the following three basic steps. Precooling the natural gas feed stream to between −30 and −40 C. Liquefaction of the natural gas stream at between −120 and −135 C. And further subcooling the liquefied natural gas to between −140 and −165 C.

Although some process cycles use the same refrigerant to perform the three steps mentioned above, the precooling step will typically be performed with a dedicated refrigerant such as propane or hydrofluorocarbon (HFC) in order to gain some cycle efficiency at the cost of extra equipment. As an option, the propane or HFC loop can be used to precool the refrigerant, or refrigerants, that are used in the natural gas liquefaction and subcooling cycles.

A typical process cycle, as known in the prior art , is indicted in FIG. 1. Natural gas feed stream 101 enters natural gas pre-cooler 102, thereby producing cooled natural gas stream 103. Cooled natural gas stream 103 enters natural gas liquefier 112, wherein it exchanges heat with cold stream 113, thereby producing liquefied natural gas stream 116, and warm stream 114. Warm stream 114 is compressed in) refrigerant compressor 115, thereby producing cold stream 113. In some cycles, a portion 117 of stream 113 is introduced into pre-cooler 102.

Pre-cooler 102 is cooled by a refrigeration loop with, typically, propane or HFC as a refrigerant. A typical mechanical refrigeration cycle is described below, but one of ordinary skill in the art would recognize that other known refrigeration cycles are also possible. Cold propane (or HFC) refrigerant stream 104, indirectly exchanges heat with natural gas feed stream 101 within pre-cooler 102, thereby producing warm propane (or HFC) refrigerant stream 105. Warm propane (or HFC) refrigerant stream 105 is then compressed in refrigerant compressor 106, thereby producing compressed propane or HFC refrigerant stream 108. In some cycles, intermediate warm propane (or HFC) refrigerant stream 107 is removed from pre-cooler 102 and introduced into refrigerant compressor 106, at some intermediate stage. Compressed propane or HFC refrigerant stream 108 is cooled and condensed in propane (or HFC) heat exchanger 109, thereby producing cool propane (or HFC) refrigerant stream 110. Cool propane (or HFC) refrigerant stream 110 is then expanded in propane (or HFC) expansion valve 111, thereby producing cold propane (or HFC) refrigerant stream 104

There is a growing interest in carbon dioxide capture from the various carbon dioxide emitters, such as powerplants, steam methane reformers, gas turbines, etc. The main outcome for carbon dioxide is typically enhanced oil recovery, underground sequestration, food and beverage application or other conversion routes such as carbon dioxide to methanol. For these applications, the carbon dioxide needs to be at a certain level of purity (which varies dependent upon the particular application). However, the carbon dioxide sources are often diluted in carbon dioxide and contain impurities that do not meet the specification of the targeted application. The carbon dioxide source typically needs to be purified via adsorption, absorption, membrane permeation or cryogenics or a combination of these technologies. If cryogenic purification is envisaged and liquefaction needs to be performed for the final carbon dioxide conditioning (for easier transportation) or the carbon dioxide needs to be compressed before being sent to the battery limit, then there is a possibility for integration of this carbon dioxide recovery unit and a natural gas liquefaction plant.

SUMMARY

A method of simultaneously liquefying CO2 and cooling natural gas, including providing a compressed CO2 loop, comprising a pressurized cooling stream, wherein a first compressed cooling stream and a second compressed cooling stream are produced by a CO2 compressor. Providing at least a portion of the first compressed cooling stream to a CO2 liquefaction system, wherein the first compressed cooling stream provides at least a portion of the refrigeration required by the CO2 liquefaction system. Providing at least a portion of the second compressed cooling stream to the pre-cooling system of a natural gas liquefaction system, wherein the second compressed cooling stream provides at least a portion of the refrigeration required by the natural gas pre-cooling.

BRIEF DESCRIPTION OF THE FIGURES

For a further understanding of the nature and objects for the present invention, reference should be made to the following detailed description, taken in conjunction with the accompanying drawings, in which like elements are given the same or analogous reference numbers and wherein:

FIG. 1 is a schematic representation of a process cycle as known in the art.

FIG. 2 is a schematic representation of one embodiment of a combined system, in accordance with one embodiment of the present invention.

FIG. 3 is a schematic representation of another embodiment of a combined system, in accordance with one embodiment of the present invention.

FIG. 4 is a schematic representation of another embodiment of a combined system, in accordance with one embodiment of the present invention.

FIG. 5 is a schematic representation of another embodiment of a combined system, in accordance with one embodiment of the present invention.

FIG. 6 is a schematic representation of another embodiment of a combined system, in accordance with one embodiment of the present invention.

ELEMENT NUMBERS

101=natural gas feed stream

102=natural gas pre-cooler

103=cooled natural gas

104=cold propane or HFC refrigerant stream

105=warm propane or HFC refrigerant stream

106=refrigerant compressor

107=intermediate warm propane or HFC refrigerant stream

108=compressed propane or HFC refrigerant stream

109=propane or HFC refrigerant heat exchanger

110=cool propane or HFC refrigerant stream

111=propane or HFC refrigerant expansion valve

112=natural gas liquefier

113=cold stream

114=warm stream

115=mixed refrigerant or nitrogen stream compressor

116=liquefied natural gas stream

117=cold stream to natural gas precooler (optional)

201=carbon dioxide containing feed stream

202=carbon dioxide capture and purification unit

203=gaseous carbon dioxide stream

204=carbon dioxide compressor

205=compressed carbon dioxide stream

206=carbon dioxide liquefaction unit

207=first portion of cold carbon dioxide refrigeration stream

208=first warm carbon dioxide refrigeration stream

209=intermediate warm carbon dioxide refrigeration stream

210=first combined warm carbon dioxide refrigeration stream

211=second warm carbon dioxide refrigeration stream

212=second combined warm carbon dioxide refrigeration stream

213=carbon dioxide refrigeration loop compressor

214=compressed carbon dioxide refrigeration stream

215=carbon dioxide refrigerant heat exchanger

216=cool carbon dioxide refrigerant stream

217=carbon dioxide refrigerant expansion valve

218=cold carbon dioxide refrigerant stream

219=second portion of cold carbon dioxide refrigeration stream

220=intermediate second warm carbon dioxide refrigeration stream

221=liquefied carbon dioxide stream

301=carbon dioxide refrigerant heat exchanger

302=cool carbon dioxide refrigerant stream

303=carbon dioxide refrigerant expansion valve

304=cold carbon dioxide refrigerant stream

305=first portion of cold carbon dioxide stream

306=second portion of cold carbon dioxide stream

307=intermediate warm carbon dioxide refrigeration stream

308=first warm carbon dioxide refrigeration stream

309=second warm carbon dioxide stream

310=combined carbon dioxide stream

401=combined gaseous carbon dioxide stream

402=carbon dioxide refrigerant heat exchanger

403=cool carbon dioxide refrigerant stream

404=carbon dioxide refrigerant expansion valve

405=cold carbon dioxide refrigerant stream

406=second portion of compressed carbon dioxide stream

407=first portion of compressed carbon dioxide stream

408=warm carbon dioxide stream

409=intermediate warm carbon dioxide stream

DESCRIPTION OF PREFERRED EMBODIMENTS

Illustrative embodiments of the invention are described below. While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and are herein described in detail. It should be understood, however, that the description herein of specific embodiments is not intended to limit the invention to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.

It will of course be appreciated that in the development of any such actual embodiment, numerous implementation-specific decisions must be made to achieve the developer's specific goals, such as compliance with system-related and business-related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming, but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure.

Carbon dioxide exhibits some interesting thermodynamic properties with the possibility to leverage the latent heat of vaporization between −56 C (at a corresponding pressure of approximately 5.2 bar abs) and 31 C (at a corresponding pressure of approximately 74 bar abs). Therefore, carbon dioxide can be used as a refrigerant instead of propane or any HFC for the precooling step of the natural gas liquefaction plant. And with the consideration of keeping the pressure of the precooling refrigerant cycle above atmospheric pressure, carbon dioxide allows to reach colder temperature than propane. Moreover, carbon dioxide is non-flammable, which is an obvious advantage in terms of safety risk and permitting aspect versus hydrocarbons.

In one embodiment of the present invention, carbon dioxide is compressed in a common compressor section and is used to precool natural gas in a natural gas liquefaction plant and to liquefy carbon dioxide captured from one or several industrial sources. Carbon dioxide at different pressure levels can be used but will be compressed in the same compression section. The pressures of the carbon dioxide refrigeration cycle will be adjusted depending on the level of cold required, but the lowest pressure of the carbon dioxide in the refrigeration loop will be above the triple point (5.2 bar abs).

Turning to FIG. 2, one embodiment of the above combined system is presented. In the interest of simplicity, the elements shared with FIG. 1 maintain the same element numbers. Carbon dioxide containing feed stream 201 is introduced into carbon dioxide capture and purification unit 202, thereby producing gaseous carbon dioxide stream 203. Carbon dioxide capture and purification unit 202 may utilize adsorption, absorption, cryogenics or/and membranes as known in the art.

Gaseous carbon dioxide stream 203 is then introduced into carbon dioxide compressor 204, thereby producing compressed carbon dioxide stream 205. Compressed carbon dioxide stream 205 is introduced into carbon dioxide liquefaction unit 206, wherein it indirectly exchanges heat with first portion of cold carbon dioxide refrigeration stream 207, thereby producing first warm carbon dioxide refrigeration stream 208, intermediate warm carbon dioxide refrigeration stream 209, and liquefied carbon dioxide stream 221.

First warm carbon dioxide refrigeration stream 208 and potentially intermediate warm carbon dioxide refrigeration stream 209 are combined, thereby forming first combined warm carbon dioxide refrigeration stream 210. First combined warm carbon dioxide refrigeration stream 210 is combined with second warm carbon dioxide refrigeration stream 211, thereby forming second combined warm carbon dioxide refrigeration stream 212. Second combined warm carbon dioxide refrigeration stream 212 and Intermediate second warm carbon dioxide refrigeration stream 220 are introduced into carbon dioxide refrigeration loop compressor 213, thereby producing compressed carbon dioxide refrigeration stream 214.

Compressed carbon dioxide refrigeration stream 214 is cooled in carbon dioxide refrigerant heat exchanger 215, thereby producing cool carbon dioxide refrigerant stream 216. Cool carbon dioxide refrigerant stream 216 is then expanded in carbon dioxide refrigerant expansion valve 217, thereby producing cold carbon dioxide refrigerant stream 218. Alternatively, the expansion valve can be located at a colder temperature level after cooling in the 206 and 102 exchangers. Cold carbon dioxide refrigerant stream 218 is split into first portion of cold carbon dioxide refrigeration stream 207 and second portion of cold carbon dioxide refrigeration stream 219.

Natural gas feed stream 101 enters natural gas pre-cooler 102, thereby producing cooled natural gas stream 103. Cooled natural gas stream 103 enters natural gas liquefier 112, wherein it exchanges heat with cold stream 113, thereby producing liquefied natural gas stream 116, and warm stream 114. Warm mixed (or nitrogen) refrigerant stream 114 is compressed in mixed refrigerant (or nitrogen) refrigerant compressor 115, thereby producing cold stream 113. In some cycles, a portion 117 of cold mixed (or nitrogen) refrigerant stream 113 is introduced into pre-cooler 102.

One of ordinary skill in the art will recognize that the refrigeration loop (as indicated in FIG. 2 by streams 207-220) could use a different refrigerant, such as propane, ammonia, or HFC, but the preferred embodiment is carbon dioxide.

Turning to FIG. 3, one embodiment of the above combined system is presented. In the interest of simplicity, the elements shared with FIGS. 1 and 2 are maintain the same element numbers. Carbon dioxide containing feed stream 201 is introduced into carbon dioxide capture and purification unit 202, thereby producing gaseous carbon dioxide stream 203. Carbon dioxide capture and purification unit 202 may utilize adsorption, absorption, cryogenics or/and membranes as known in the art.

Gaseous carbon dioxide stream 203 is then introduced into carbon dioxide compressor 204, thereby producing compressed carbon dioxide stream 205. Compressed carbon dioxide stream 205 is introduced into carbon dioxide liquefaction unit 206, wherein it indirectly exchanges heat with cold carbon dioxide refrigerant stream 218 and natural gas feed stream 101, thereby producing first warm carbon dioxide refrigeration stream 208, intermediate warm carbon dioxide refrigeration stream 209, cooled natural gas stream 103, and liquefied carbon dioxide stream 221.

First warm carbon dioxide refrigeration stream 208 and intermediate warm carbon dioxide refrigeration stream 209 are combined, thereby forming first combined warm carbon dioxide refrigeration stream 210. First combined warm carbon dioxide refrigeration stream 210 is introduced into carbon dioxide refrigeration loop compressor 213, thereby producing compressed carbon dioxide refrigeration stream 214. Compressed carbon dioxide refrigeration stream 214 is cooled in carbon dioxide refrigerant heat exchanger 215, thereby producing cool carbon dioxide refrigerant stream 216. Cool carbon dioxide refrigerant stream 216 is then expanded in carbon dioxide refrigerant expansion valve 217, thereby producing cold carbon dioxide refrigerant stream 218.

Cooled natural gas stream 103 enters natural gas liquefier 112, wherein it exchanges heat with cold stream 113, thereby producing liquefied natural gas stream 116, and warm mixed (or nitrogen) refrigerant stream 114. Warm mixed (or nitrogen) refrigerant stream 114 is compressed in mixed refrigerant (or nitrogen) refrigerant compressor 115, thereby producing cold stream 113.

One of ordinary skill in the art will recognize that the refrigeration loop (as indicated in FIG. 3 by streams 207-220) could use a different refrigerant, such as propane, ammonia, or HFC, but the preferred embodiment is carbon dioxide.

Turning to FIG. 4, another embodiment of the proposed combined system is presented. In the interest of simplicity, the elements shared with FIGS. 1 and 2 maintain the same element numbers, Carbon dioxide containing feed stream 201 is introduced into carbon dioxide capture and purification unit 202, thereby producing gaseous carbon dioxide stream 203. Carbon dioxide capture and purification unit 202 may utilize adsorption, absorption, cryogenics or/and membranes as known in the art.

Gaseous carbon dioxide stream 203 is combined with second warm carbon dioxide stream 309, then combined carbon dioxide stream 310 is introduced into carbon dioxide compressor 204, thereby producing compressed carbon dioxide stream 205. Compressed carbon dioxide stream 205 is cooled in carbon dioxide refrigerant heat exchanger 301 thereby producing cool carbon dioxide refrigerant stream 302. Cool carbon dioxide refrigerant stream 302 is then expanded in carbon dioxide refrigerant expansion valve 303 thereby producing cold carbon dioxide refrigerant stream 304. Cold carbon dioxide refrigerant stream 304 is split into first portion of cold carbon dioxide refrigeration stream 305 and second portion of cold carbon dioxide refrigeration stream 306.

Second portion of cold carbon dioxide refrigeration stream 306 is introduced into carbon dioxide liquefaction unit 206, thereby producing first warm carbon dioxide refrigeration stream 308, intermediate warm carbon dioxide refrigeration stream 307, and liquefied carbon dioxide stream 221.

Natural gas feed stream 101 enters natural gas pre-cooler 102, wherein it exchanges heat with first portion of cold carbon dioxide refrigeration stream 305, and optionally cold mixed refrigerant stream to natural gas precooler 117, thereby producing cooled natural gas stream 103 and second warm carbon dioxide stream 309. Cooled natural gas stream 103 enters natural gas liquefier 112, wherein it exchanges heat with cold mixed (or nitrogen) refrigerant stream 113, thereby producing liquefied natural gas stream 116, and warm mixed (or nitrogen) refrigerant stream 114. Warm mixed (or nitrogen) refrigerant stream 114 is compressed in mixed refrigerant (or nitrogen) refrigerant compressor 115, thereby producing cold stream 113. In some cycles, a portion 117 of cold mixed (or nitrogen) refrigerant stream 113 is introduced into pre-cooler 102.

Turning to FIG. 5, another embodiment of the proposed combined system is presented. In the interest of simplicity, the elements shared with FIGS. 1, 2, and 4 maintain the same element numbers. Carbon dioxide containing feed stream 201 is introduced into carbon dioxide capture and purification unit 202, thereby producing gaseous carbon dioxide stream 203. Carbon dioxide capture and purification unit 202 may utilize adsorption, absorption, cryogenics or/and membranes as known in the art.

Gaseous carbon dioxide stream 203 is introduced into carbon dioxide compressor 204, thereby producing compressed carbon dioxide stream 205. Compressed carbon dioxide stream 205 is cooled in carbon dioxide refrigerant heat exchanger 301 thereby producing cool carbon dioxide refrigerant stream 302. Cool carbon dioxide refrigerant stream 302 is then expanded in carbon dioxide refrigerant expansion valve 303 thereby producing cold carbon dioxide refrigerant stream 304.

Cold carbon dioxide refrigeration stream 304 is introduced into carbon dioxide liquefaction unit 206, wherein it and natural gas feed stream 101 are cooled, thereby producing first warm carbon hereby producing first warm carbon dioxide refrigeration stream 308, intermediate warm carbon dioxide refrigeration stream 307, cooled natural gas stream 103, and liquefied carbon dioxide stream 221.

Cooled natural gas stream 103 enters natural gas liquefier 112, wherein it exchanges heat with cold stream 113, thereby producing liquefied natural gas stream 116, and warm mixed (or nitrogen) refrigerant stream 114. Warm mixed (or nitrogen) refrigerant stream 114 is compressed in mixed refrigerant (or nitrogen) refrigerant compressor 115, thereby producing cold stream 113.

Turning to FIG. 6, another embodiment of the proposed combined system is presented. In the interest of simplicity, the elements shared with FIGS. 1 and 2 maintain the same element numbers. Carbon dioxide containing feed stream 201 is introduced into carbon dioxide capture and purification unit 202, thereby producing gaseous carbon dioxide stream 203. Carbon dioxide capture and purification unit 202 may utilize adsorption, absorption, cryogenics or/and membranes as known in the art.

Gaseous carbon dioxide stream 203 is combined with intermediate warm carbon dioxide stream 409, then combined carbon dioxide stream 401 and warm carbon dioxide stream 408 are is introduced into carbon dioxide compressor 204, thereby producing compressed carbon dioxide stream 205. Compressed carbon dioxide stream 205 is cooled in carbon dioxide refrigerant heat exchanger 401 thereby producing cool carbon dioxide refrigerant stream 403. Cool carbon dioxide refrigerant stream 403 is then expanded in carbon dioxide refrigerant expansion valve 404 thereby producing cold carbon dioxide refrigerant stream 405. Cold carbon dioxide refrigerant stream 405 is split into first portion of cold carbon dioxide refrigeration stream 407 and second portion of cold carbon dioxide refrigeration stream 406.

Natural gas feed stream 101 enters natural gas pre-cooler 102, wherein it exchanges heat with first portion of cold carbon dioxide refrigeration stream 407, and optionally cold mixed refrigerant stream to natural gas precooler 117, thereby producing cooled natural gas stream 103 and warm carbon dioxide stream 408. Cooled natural gas stream 103 enters natural gas liquefier 112, wherein it exchanges heat with cold mixed (or nitrogen) refrigerant stream 113, thereby producing liquefied natural gas stream 116, and warm mixed (or nitrogen) refrigerant stream 114. Warm mixed (or nitrogen) refrigerant stream 114 is compressed in mixed refrigerant (or nitrogen) refrigerant compressor 115, thereby producing cold mixed (or nitrogen) refrigerant stream 113. In some cycles, a portion 117 of cold mixed (or nitrogen) refrigerant stream 113 is introduced into pre-cooler 102. 

What is claimed is:
 1. A method of simultaneously liquefying CO2 and cooling natural gas, comprising: providing a compressed CO2 loop, comprising a pressurized stream, wherein a first compressed stream and a second compressed stream are produced by a CO2 compressor, providing at least a portion of the first compressed stream to a CO2 liquefaction system, wherein the first compressed stream provides at least a portion of the refrigeration required by the CO2 liquefaction system, providing at least a portion of the second compressed stream to the pre-cooling system of a natural gas liquefaction system, wherein the second compressed stream provides at least a portion of the refrigeration required by the natural gas pre-cooling.
 2. The method of claim 1, wherein the lowest pressure within the CO2 loop is greater than the triple point pressure of CO2.
 3. The method of claim 1, wherein the CO2 liquefaction system comprises at least one recycle stream that is introduced into the CO2 compressed CO2 loop.
 4. The method of claim 1, wherein the first compressed cooling stream and the second compressed cooling stream are at the same pressure.
 5. The method of claim 1, wherein the first compressed cooling stream and the second compressed cooling stream are at different pressures.
 6. A method of simultaneously producing a pressurized CO2 stream and cooling natural gas, comprising: providing a CO2 compressor system, comprising at least a first compressed stream and a second compressed stream, wherein the first compressed stream and the second compressed stream are produced by a CO2 compressor, providing at least a portion of the first compressed stream to a downstream user, providing at least a portion of the second compressed stream to the pre-cooling system of a natural gas liquefaction system, wherein the second compressed stream provides at least a portion of the refrigeration required by the natural gas pre-cooling.
 7. The method of claim 6, wherein the lowest pressure within the CO2 loop is greater than the triple point pressure of CO2.
 8. The method of claim 6, wherein the downstream user is an enhanced oil recovery system.
 9. The method of claim 6, wherein the downstream user is a CO2 sequestration system. 